The stoichiometric photobioreaction model can be used to simulate a sequence of continuous reactions that take place in a photobioreactor (e.g., Raceway Pond) when the reaction kinetics are unknown or unimportant but the mass stoichiometry is known and the extent of reaction can be specified or calculated based on the concentration of a reference component. The extent of reaction is defined as the fractional conversion of the limiting component.
● Continuous Stoichiometric Reaction Procedure in a Raceway Pond
When the gas supply is set by the user (expressed as volume of gas under standard conditions per volume of reactant mixture per minute - VVM), the flowrate of the gas supply stream is adjusted by the operation. If the gas supply stream has a source unit procedure (e.g., a compressor), then the adjustment of its flowrate is recursively back - propagated till process feed streams are reached. At least one of the process feed streams that feed into the gas supply stream must have non-zero flowrate. Only units with a single output stream can be part of the sequence of units that feed into a gas supply stream. An exception to this rule is the ‘Custom Mixer’ which is not allowed to be part of the sequence even though it has a single output stream.
In terms of sorption, you may specify the percent fraction of a component that adsorbs on the primary biomass component (‘Sorption %’) through the Sorption tab. The program, then, keeps track of the fraction in solution throughout the process with the ‘Extra-Cell %’ term. The ‘Extra-Cell %’ term represents the percentage of a component that is in solution while 100 - Extra-Cell% (the intra-cellular percentage) represents the adsorbed portion of a component.
Please note that the ‘Sorption %’ cannot be set for pure components that appear as reaction products in reactions that also produce the primary biomass component. For these reactions, you can set the ‘Extra-Cell %’ of the produced amount of each product component through the reaction’s ‘Stoichiometry Balance Table’. For each pure component that appears in at least one such reaction, the program will then calculate the ‘Sorption %’ in the liquid product stream.
The reactions are assumed to occur in a sequence (one after the other). In that sense, the calculations assume that the product mixture of the first reaction is the reacting mixture of the second, and so on.
The user provides the mass or molar stoichiometric coefficients (Ai) of the various components for each reaction and the extent of reaction based on either the limiting component or a reference component. The algorithm used by the program to perform the material balances for each reaction is explained in the following paragraphs.
If the extent of the reaction is expressed based on the limiting component then, first of all, the limiting component is identified. This is done based on the mass stoichiometry and the composition of the reacting mixture. If the extent of the reaction is expressed based on a user-defined component, then first of all, the program attempts to validate that the user-defined conversion is achievable (i.e., there are enough reactants for the reaction to proceed to such an extent). If that is not the case, then the conversion is adjusted to reflect the maximum achievable conversion percentage (based on the extent-reference component chosen by the user).
For the limiting component (k) or the extent-reference component (depending on what is the case) the following holds:
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where:
● Fout,k is the mass flowrate of the component after the reaction,
● Fin,k is the mass flowrate of the component before the reaction, and
● x is the (possibly adjusted) reaction extent.
For any other component, the mass flow rate after the reaction can be calculated as follows:
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where:
● Fout,i is the mass flowrate of component “i” after the reaction,
● Fin,i, Fin,k are the mass flowrates of components “i” and “k” (limiting component), respectively, and
● Ai, Ak are the stoichiometric coefficients of components “i” and “k” (limiting component), respectively.
The above calculations are repeated for all reactions specified using the product mixture after each reaction as feed for the next reaction.
See Vessel Sizing (Continuous Operations).
You may also specify the percentage of each component (at the end of all reactions) that ends up in the gas exhaust stream through the Cont. Stoich. Reaction in a Photobioreactor: Vent/Emissions Tab.
See Vacuum Pump Auxiliary Equipment Calculations.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Continuous Fermentation Operations: Oper. Conds Tab
● Volumes, see Continuous Vessel Operations (Design Mode): Volumes Tab and Continuous Vessel Operations (Rating Mode): Volumes Tab
● Reactions, see Stoichiometric Reaction/Fermentation Operation: Reactions Tab
● Split, see Continuous Reaction / Storage Operations: Split Tab
● Vent/Emissions, see Cont. Stoich. Reaction in a Photobioreactor: Vent/Emissions Tab
● Sorption, see Environmental Reaction Operations: Sorption Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab
